ci(github): prune stale nightly APKs from FTP latest folder after upload

[kryoseu]

Contribution Summary

Linked Issue/Ticket: N/A

Description

Currently, the nightly latest FTP is keeping both latest and previous builds, whereas we want to keep latest only.

This adds a post-upload cleanup step that removes old files from the nightly latest FTP destination, keeping only the current APK and tar — preventing accumulation of stale builds.

I have tested the proposed gcloud command against my own bucket:

• Copied 4 files into the bucket:

❯ gcloud storage cp thunderbird-2* gs://test-bucket-ebaginski
Copying file://thunderbird-20-0a1.apk to gs://test-bucket-ebaginski/thunderbird-20-0a1.apk
Copying file://thunderbird-20-0a1.tar.gz to gs://test-bucket-ebaginski/thunderbird-20-0a1.tar.gz
Copying file://thunderbird-21-0a1.apk to gs://test-bucket-ebaginski/thunderbird-21-0a1.apk
Copying file://thunderbird-21-0a1.tar.gz to gs://test-bucket-ebaginski/thunderbird-21-0a1.tar.gz

• Prune stale ones:

❯ FTP_DESTINATION_NIGHTLY_LATEST=test-bucket-ebaginski
❯ PKG_FILE=thunderbird-21-0a1.apk
❯ FTP_TAR_FILENAME=thunderbird-21-0a1.tar.gz
❯ gcloud storage ls "gs://${FTP_DESTINATION_NIGHTLY_LATEST}/" \
            | grep -vF "${PKG_FILE}" \
            | grep -vF "${FTP_TAR_FILENAME}" \
            | xargs -r gcloud storage rm

Removing objects:

Removing gs://test-bucket-ebaginski/thunderbird-20-0a1.apk...
Removing gs://test-bucket-ebaginski/thunderbird-20-0a1.tar.gz...

• Result:

❯ gcloud storage ls "gs://${FTP_DESTINATION_NIGHTLY_LATEST}/"
gs://test-bucket-ebaginski/thunderbird-21-0a1.apk
gs://test-bucket-ebaginski/thunderbird-21-0a1.tar.gz

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[github-actions]

✅ Validation Passed: All report and feature-flag labels are correctly set.

[coreycb]

This is great. Thanks for the fix. It mostly looks good. I add a couple of comments inline.